The Battle of Chosin Reservoir, also known as the Chosin Reservoir Campaign or the Changjin Lake Campaign (Korean: 장진호 전투; hanja: 長津湖戰鬪; rr: Jangjin ho jeontu; Chinese: 长津湖战役; pinyin: Cháng Jīn Hú Zhànyì), was a decisive battle in the Korean War.
In both the novel First Blood and as according to the film's Survival Mode, Will Teasle was a veteran of the Chosin Reservoir. He was awarded the "Distinguished Service Cross for "conspicuous and valiant leadership" for his role in the battle.
The name "Chosin" is derived from the Japanese pronunciation "Chōshin" of the Chinese word 長津. The UN forces relied on Japanese language maps dating from their occupation of Korea which had only ended five years earlier at the conclusion of World War II. Shortly after the People's Republic of China entered the conflict, the People's Volunteer Army 9th Army infiltrated the northeastern part of North Korea.
On 27 November 1950, the Chinese 9th Army surprised the US X Corps commanded by Major General Edward Almond at the Chosin Reservoir area. A brutal 17-day battle in freezing weather soon followed. In the period between 27 November and 13 December, 30,000 United Nations troops (later nicknamed "The Chosin Few") under the field command of Major General Oliver P. Smith were encircled and attacked by approximately 120,000 Chinese troops under the command of Song Shi-Lun, who had been ordered by Mao Zedong to destroy the UN forces. The UN forces were nonetheless able to make a fighting withdrawal and broke out of the encirclement while inflicting crippling losses on the Chinese. The evacuation of the X Corps from the port of Hungnam marked the complete withdrawal of UN troops from North Korea.